The present invention relates to a process for forming a metal or metal compound coating on a face of a hot vitreous substrate in sheet or ribbon form by continually advancing the substrate in a given direction (hereafter called "downstream direction") along a path through a coating station, discharging droplets of liquid coating precursor material in the downstream direction so that such material contacts the substrate at said coating station, continuously withdrawing vapours from the coating station in the downstream direction and thereafter annealing the substrate.
Processes of the foregoing kind are used for example as described in British specification No. 1 516 032 for forming surface coatings which modify the apparent colour of the glass and/or which confer some other required property in respect of incident radiation, e.g. an infra-red-reflecting property.
The coating precursor material is applied in the liquid phase, for example in solution as described in British Patent Specification No. 1 523 991.
In some processes of the kind above referred to, the discharged coating precursor material is a single precursor substance, and in other such processes it comprises more than one coating precursor substance, for example a main coating constituent precursor and a coating additive precursor. Where more than one such precursor substance is discharged onto the substrate, they may be discharged in admixture, or separately for example as referred to in BFG Glassgroup's British Patent Application No. 81 18 611 (Publication No. GB 2 078 213A).
Processes as referred to are particularly useful for forming metal oxide coatings on ribbons of glass during their conveyance from a flat glass forming installation, e.g. a drawing machine or a float tank.
It is not easy to form coatings satisfying the high quality standards which the market sometimes demands.
One important problem which is encountered is non-uniformity in the adherence of the coating to the glass. Another problem is non-uniformity of the internal structure of the coating formed. It has been found that the difficulties posed by these problems increase with an increase in the rate of application of the coating precursor material, so that they are particularly severe when applying thick coatings and/or when the substrate is advanced rapidly through the coating station, for example when coating a freshly formed ribbon of float glass.